Fall Garden Prep for the Native Plant Garden 

The leaves are starting to turn colour, the air is getting cooler, and there are lots of gardening articles being written about what to do with your Canna Lilies and rose bushes and dahlias for the winter. But what about those of us who grow native plants? Do we have to do anything to prepare our plants and flower beds for winter? After all, Mother Nature has been looking after herself for millennia. 

How much fall prep you do will depend primarily on WHY you grow native plants.  

Leave the Plant Stalks 

When I started growing natives, I came from a background of conventional gardening, and the easiest way to put my native plant gardens to bed for the winter was to simply set my mulching mower as high as it would go and mow everything down. The result was a tidy looking flower bed that was ready to emerge in the spring.  

In the spring, after an extensive fall clean up, the flowerbeds looked tidy, but there was no shelter for overwintering insects.

Unfortunately, I also removed important habitat for bees and other insects. 

As my understanding grew of the importance of leaving stems for leaf cutter and wool carder bees and for small carpenter bees and others, I had to change my mind set. I started to leave a few of the pithy stems of Monarda (Bee Balm and Wild Bergamot) but I still “cleaned up” the rest of the flower beds by cutting down the asters, Joe Pye weed, coneflowers, etc. and hauling the debris to the municipal yard for composting.  

Leaving those stems was really hard to do – at first. It offended my sensibilities as to what a neat and tidy garden should look like for the winter. But whether it was my imagination or reality, I thought I detected more bees the next year, and more species of bees as well. So when fall rolled around again I compromised – I cut down most of the plants to about 18”, and rather than hauling the debris away, I cut it into 1-2’ lengths and left it on the ground.

Because my gardens are very densely planted, and some with very tall plants, I would have had a foot of cuttings if I dropped them all in the garden, so I kept it to a minimum by leaving one thin layer in the flowerbed, and placing the remaining stems in an out of the way corner of the yard. 

Surprisingly, it was my mindset that had the greatest change as a result of this new strategy. I no longer saw a “mess” in the flowerbed in the fall. Instead, I saw potential habitat. I saw that I was giving Mother Nature a helping hand. It’s one thing to provide native plants for bees, butterflies and caterpillars to feed on during the summer, but if you don’t provide them with a place to overwinter, then you are really only helping those species that migrate. 

Leaving the flower stalks has, in addition to the wildlife benefit, the added beauty of great structure in the winter garden. 

But is leaving the stems the only thing we can do?  

Leave the Leaves 

Leaving the leaves on our lawns is just about as difficult to do as leaving plant stems in the gardens for the winter for most of us. But it is just as important. I do rake my lawn in the fall, but I have much less area of lawn than I do of flowerbeds, so the leaves get raked onto the beds. They provide mulch to keep annual weeds down in the spring, and fertilizer as the leaves decay. And depending on the bed, I may put just a thin layer (on the beds of prairie species, for example) or a layer at least 6” thick under the sugar maples where Trilliums, Jack in the Pulpit, and other spring ephemerals need the organic matter and moisture retaining quality of the decaying leaves.  

Most of our spring forest wildflowers require deep, humus-rich soils to flourish. Decaying leaves provide this.

I actually have so many trees in my yard now that I now create piles of the excess leaves in the fall to be spread over the shade garden in mid-May when most of the leaves there have been consumed by insects, worms and microbes.  

But why is it important to leave the leaves, other than for mulch and natural fertilizer? 

For starters, many of our butterflies and some of our more spectacular moths overwinter in the leafy debris. 

According to the Royal Ontario Museum’s book Butterflies of Ontario, of the 127 species of butterflies in this province, 110 overwinter here.  

  • 6 overwinter as adults 
  • 12 overwinter as eggs 
  • 30 overwinter as a chrysalis 
  • 60 overwinter as a caterpillar, and  
  • 2 overwinter as either a caterpillar or a chrysalis. 

Many of these hide either in the leaf litter or in the ground (where the leaf litter helps to keep them warm). 

Many of our moths do the same. The ones we tend to get excited about – the large, showy ones – are no different. For instance, the beautiful green Luna Moth overwinters by using its silk to bind dead leaves around its cocoon. The Virgin Tiger Moth overwinters as a caterpillar, hiding in the leaf litter. And as for everyone’s favourite – the Hummingbird Clearwing Moth – the fully-grown caterpillars burrow in the leaf litter to pupate, emerging soon after and overwintering as an adult, or waiting in the cocoon until the following spring to emerge.  

So the less we can disturb the leaf litter, the better, as far as I am concerned.  

Do it for the Bees, Too 

We also have a number of ground nesting bees that greatly benefit from a quilt of leaves to help maintain a comfortable temperature all winter long. The leaves have the added benefit of slowing down the heating of the soil in a January thaw that might cause the bees to emerge too early before any food sources are available. 

The American Sand Wasp (Bembix americana) is just one of many ground nesting bees and wasps. These wasps are solitary predators that primarily target flies – including the annoying horse and deer flies – for their developing larvae. When the larvae mature, the tunnel is sealed for the winter. They pupate in spring and come out from their tunnels in summer.

As you start thinking about preparing your garden for its long winter rest, think of the insects that need the stems and leaves to survive till spring. Leave some stems, and leave the leaves.